Hermetic compressors are designated high side or low side depending upon whether a major portion of the shell or casing is filled with discharge gas or suction gas, respectively. Since suction gas is delivered through the shell to the compressor and discharge gas is delivered from the compressor through the shell to the refrigeration system, it is necessary to keep the two flows isolated from each other. In high side compressors, for example, it is common to deliver the suction gas via a suction line directly to the compression chamber and to pass the compressed gas to the interior of the shell and then out the discharge line. For low side compressors, if an internal muffler is desired, there must be a portion of the shell at discharge pressure unless the casing is enlarged to provide for the placement of a sealed muffler therein and the heat transfer between the muffler and suction gas is ignored. For scroll compressors, a check valve must be located in the discharge passage to prevent the compressor from running as an expander due to the reversed pressure differential upon stopping.